Fix RecurMixin by making it an abstract model

core/mixins/billable.py

@@ -1,4 +1,4 @@
-from django.db.models import PositiveIntegerField, DateField, IntegerChoices
+from django.db.models import PositiveIntegerField, DateField, IntegerChoices, Model
 
 class ActionChoices(IntegerChoices):
     WAIT = 0, "Do not invoice for now"
@@ -13,7 +13,10 @@ class CycleChoices(IntegerChoices):
     MONTHS = 2, "Months"
     YEARS = 3, "Years"
 
-class RecurMixin:
+class RecurMixin(Model):
+    class Meta:
+        abstract = True
+
     date = DateField()
     recur_action = PositiveIntegerField(choices=ActionChoices.choices)
     recur_cycle = PositiveIntegerField(choices=CycleChoices.choices)

core/models/services.py

@@ -2,6 +2,7 @@ from core.fields.numbers import CostField
 from core.models.local import Currency
 from core.models.profiles import ClientProfile
 from core.models.billable import BaseBillable
+from core.mixins.billable import RecurMixin
 
 from django.db.models import Model, TextField, CharField, ManyToManyField, ForeignKey, CASCADE, PositiveIntegerField, OneToOneField, BooleanField, SET_NULL
 
@@ -38,5 +39,5 @@ class ServicePlan(Model):
         for item in productplan.serviceplanitem_set:
             ServicePlanItem.objects.create(plan=plan, cycle=item.cycle, count=item.count, cost=item.cost)
 
-class ServicePlanItem(BaseBillable): 
+class ServicePlanItem(RecurMixin, BaseBillable): 
     plan = ForeignKey(ServicePlan, on_delete=CASCADE)